1. Field of the Invention
The present invention relates to an aerostatic bearing, and more particularly, to a porous aerostatic bearing.
2. Background of the Invention
With reference to FIG. 1, a conventional porous aerostatic bearing includes a substrate 11 and a porous layer 12 disposed under the substrate 11, wherein the substrate 11 includes a through hole 111 communicating with the porous layer 12. Air can transmit into the porous layer 12 via the through hole 111, and an gas membrane is generated when the air passes through the micro pores of the porous layer 12. Therefore, the aerostatic bearing is spaced apart from a platform 13 and floats on the platform 13.
There are several types of conventional restrictive technologies in the field of aerostatic bearing. For the aerostatic bearing with the form of porous restriction, the device surface is filled with micro openings and its micro-porosity structure may have excellent fluid damping characteristic, which possesses better performance of gas-membrane rigidity, bearing capacity and dynamic stability, compared with the pore type, slit type or slot type aerostatic bearing. When the porous aerostatic bearing is applied as a plane bearing of straight slideway or a rotation bearing of precision spindle, the porous aerostatic bearing possesses the advantages of simple design, miniature, ultra precision and high dynamic stability.
In the pressure distribution of gas membrane within all types of restriction technologies, the gas membrane generated by aerostatic bearing with the form of porous restriction theoretically possesses the highest bearing capacity, stability and uniformity. However, the features of the pore size, porosity and penetrance in porous material are not distributed uniformly due to manufacture variance. Since the pore size and porosity are the key factors to effect permeability of air, if the permeability of air is not uniform, the bearing capacity and stability will be affected as well. In addition, in a conventional porous aerostatic bearing, when the porous material is made, its air permeability is determined already. That is to say, the air permeability cannot be adjusted in the conventional porous aerostatic bearing. Accordingly, the porous aerostatic bearing still faces difficulties in practical industrial application.